The widely-used peripheral input device of a computer system comprises for example a mouse device, a keyboard device, a trackball device, or the like. With the progress of the times, a touch pad has been introduced into the market. By directly using the user's fingers or using a touch pen to operate the touch input device, the computer system or other appropriate electronic device can be correspondingly controlled.
Nowadays, the commercially available touch pads are classified into several types, including a resistive touch pad, an acoustic wave touch pad, an infrared touch pad and a capacitive touch pad. The operating principles of these touch pads will be shortly illustrated. When a pressing object (e.g. the user's finger) is placed on the resistive touch pad, a voltage is generated and the pressing position is recognized according to the voltage. Moreover, acoustic waves pass over the surface of the acoustic wave touch pad. By touching the surface of the acoustic wave touch pad, the travelling path of the acoustic wave is blocked by the pressing object and thus the position of the pressing point is recognized. Similarly, infrared rays pass over the surface of the infrared touch pad. By touching the surface of the infrared touch pad, the travelling path of the infrared rays is blocked by the pressing object and thus the position of the pressing point is recognized. When the user's finger is contacted with the capacitive touch pad, the capacitance value of the touch point of the capacitive touch pad is subjected to a change. According to the change of the capacitance value, the position of the touch point is recognized. In views of the touch accuracy and the fabricating cost, the capacitive touch pad is widely adopted by most users.
With increasing development of the capacitive touch pad, a capacitive touch pen for the capacitive touch pad has been introduced into the market. FIG. 1 is a schematic cross-sectional view of a conventional capacitive touch pen. As shown in FIG. 1, the conventional capacitive touch pen 1 comprises a conductive pen tip 11, a metallic main body 12, a pressure sensor 13, a spiral spring 14, a circuit board 15, an actuating button 16, two triggering switches 17 and a battery 18. The conductive pen tip 11 is located at an end of the metallic main body 12 and partially exposed outside the metallic main body 12. A first end 111 of the conductive pen tip 11 may be contacted with a capacitive touch pad (not shown). A second end 112 of the conductive pen tip 11 may be contacted with the pressure sensor 13. The spiral spring 14 is sheathed around the second end 112 of the conductive pen tip 11 and contacted with the pressure sensor 13. In case that the pressure sensor 13 is pushed by the second end 112 of the conductive pen tip 11, the pressure sensor 13 generates a touch signal. The circuit board 15 is disposed within the metallic main body 12. The pressure sensor 13 and the two triggering switches 17 are connected with the circuit board 15. The actuating button 16 is disposed on the metallic main body 12 and partially exposed outside the metallic main body 12. The actuating button 16 is contacted with the actuating button 16. The battery 18 is electrically connected with the two triggering switches 17 for providing electric power to the circuit board 15.
When the actuating button 16 is pressed by the user, the two triggering switches 17 are pushed by the actuating button 16. Consequently, the two triggering switches 17 generate an signal to the circuit board 15 in order to activate the capacitive touch pen 1. After the capacitive touch pen 1 is activated, the user may grasp the capacitive touch pen 1 and allow the first end 111 of the conductive pen tip 11 to be contacted with the capacitive touch pad. Consequently, the conductive pen tip 11 is moved relative to the metallic main body 12 in the direction toward the pressure sensor 13, and the spiral spring 14 is compressed to accumulate an elastic force. On the other hand, the pressure sensor 13 is pushed by the second end 112 of the conductive pen tip 11. Consequently, the pressure sensor 13 generates the touch signal and transmits the touch signal to the conductive pen tip 11. Under this circumstance, the capacitance value of the touch point between the capacitive touch pad and the conductive pen tip 11 is changed. According to the change of the capacitance value, the capacitive touch pad may recognize the position of the touch point and generate a corresponding command.
When the capacitive touch pen 1 is moved away the capacitive touch pad, the first end 111 of the conductive pen tip 11 is no longer contacted with the capacitive touch pad. Under this circumstance, the compressed spiral spring 14 releases the elastic force so as to push the conductive pen tip 11. Consequently, the conductive pen tip 11 is moved relative to the metallic main body 12 in the direction away from the pressure sensor 13, and the conductive pen tip 11 is returned to the original position before being pushed.
However, the conventional capacitive touch pen 1 still has the following two drawbacks. Firstly, due to the structure of the conventional capacitive touch pen 1, the pressure sensor 13 is readily suffered from failure. For example, if the conventional capacitive touch pen 1 falls down to a table surface or a floor because of the user's carelessness, the first end 111 of the conductive pen tip 11 is strongly collided by the table surface or the floor, and the pressure sensor 13 is strongly collided by the second end 112 of the conductive pen tip 11.
Secondly, the pressure sensor 13 can detect the pressing force applied by the user and generate different touch signals according to different intensities of the pressing force. According to different touch signals, the conventional capacitive touch pen 1 can generate different effects. For example, if a normal pressing force is applied by the user, a line with a normal thickness may be drawn by the conventional capacitive touch pen 1. Whereas, if a stronger pressing force is applied by the user, a thicker line may be drawn by the conventional capacitive touch pen 1. However, the intensities of the pressing force received by the pressure sensor 13 and the intensities of the generated touch signals are not in a linear relationship.
For example, if a normal pressing force (e.g. 100 g) is applied by the user, a line with a normal thickness may be drawn by the conventional capacitive touch pen 1. However, if a pressure force of 200 g is applied by the user, a line with the normal thickness is also drawn by the conventional capacitive touch pen 1. Until a pressure force of 400 g is applied by the user, a thicker line may be drawn by the conventional capacitive touch pen 1. As mentioned above, if the difference between the intensities of the pressing force applied by the user is not very large, the lines drawn by the conventional capacitive touch pen 1 have the same thickness because the intensities of the touch signals outputted from the pressure sensor 13 are non-linear. Since the lines with the same thickness may be drawn in response to different intensities of the pressing force, the use of the conventional capacitive touch pen 1 perplexes the user.
Therefore, there is a need of providing an improved touch pen for reducing the failure probability and avoiding perplexing the user.